Digital trigger

Abstract

A digital trigger for a digitizing instrument having multiple analog-to-digital converters employed in interleaved fashion and in which the clock phase and period of a trigger point can be accurately determined. The digital trigger includes a digital comparator for comparing the output signals of each analog-to-digital converter to a trigger threshold level to generate a trigger signal at the output of the comparator if a trigger point occurs on the output signal. The outputs of the collective digital comparators are routed to decoding logic which generates a digital signal that indicates the phase of the clock period in which the trigger point occurred. The outputs of collective digital comparators are also logically ORed together for detecting if a trigger point occurred during a clock period.

I claim: 
     
       1. A digital trigger, comprising: a plurality of analog-to-digital converters for sampling an analog signal, each of said converters sampling the analog signal at a different phase of a clock period;   comparator means for comparing the output signal of each analog-to-digital converter to a trigger threshold level to generate a trigger signal if a trigger point occurs on the output signal; and   means for evaluating the output signals of the collective comparator means generated during the same clock period to determine the clock phase in which the trigger point occurred.   
     
     
       2. The digital trigger of claim 1 wherein the evaluating means comprises decoding logic coupled to the comparator means for generating a signal that indicates the phase of the clock period in which the trigger point occurred. 
     
     
       3. The digital trigger of claim 1 including a multiphase clock circuit having a plurality of clocks each clocking an analog-to-digital converter during a different phase of the multiphase clock period. 
     
     
       4. The digital trigger of claim 1 wherein the comparator means comprises a digital comparator for comparing the digitized value of a trigger threshold level against the digitized output signal of the analog-to-digital converter, the comparator generating a trigger signal if the digitized output signal exceeds the value of the trigger threshold level.   
     
     
       5. The digital circuit of claim 1 including means for detecting if a trigger signal occurred during a clock period. 
     
     
       6. A digital trigger for a digitizing instrument, comprising: a clock circuit having a plurality of separate clocks each generating a clock pulse during a different phase of a clock period and a system clock for generating a system clock signal defining the clock period;   a plurality of analog-to-digital converters for sampling an analog signal, each of said converters clocked by the signal of a different clock so as to sample the analog signal during each phase of the clock period;   a digital comparator for comparing the output signal of each analog-to-digital converter to a trigger threshold level to generate a trigger signal at the output of the comparator means if a trigger point occurs on the output signal;   means for evaluating the output signals of the digital comparators to determine the clock phase in which a trigger point occurred; and   means for detecting if a trigger point occurred during a clock period.   
     
     
       7. The digital trigger of claim 6 wherein the comparator means comprises: a data register for accepting the output signal of the analog-to-digital converter on the clock signal of the separate clock;   synchronization circuitry clocked to receive the output signal from the data register on each clock signal of the system clock to synchronize the output signals of the analog-to-digital converters;   a storage register clocked to receive the output signal from the synchronization circuitry on a clock signal of the system clock;   and   a digital comparator for comparing the digital value of a trigger threshold level against the output signal within the storage register, the comparator generating a trigger signal if the output signal exceeds the value of the trigger threshold level.   
     
     
       8. In a digitizing instrument wherein the instrument includes a plurality of analog-to-digital converters for sampling an analog signal, each of said converters sampling at a different phase of a clock period, a method of determining the phase of the clock period in which a trigger point occurs, comprising: comparing the digital output signal of each analog-to-digital converter means against a trigger threshold level to generate a trigger signal if a trigger point occurs on the output signal; and   evaluating the results of the above comparisons generated during a clock period to determine in which phase a trigger point occurred.   
     
     
       9. The method of claim 8 including synchronizing the output signals of the analog-to-digital converters before evaluation. 
     
     
       10. The method of claim 8 including logically ORing the results of the above comparisons to determine if a trigger point occurred during a clock period.